The present invention pertains to the field of disk drives. More particularly, this invention pertains to a method and apparatus for adjusting the torque constant of the disk drive voice coil motor to compensate for changes in temperature between calibrations in order to improve seek performance for a disk drive.
One of the key components of a computer system is a place to store data. Typically computer systems employ a number of storage means, including a disk drive which is also called a direct access storage device (DASD). A disk drive or direct access storage device includes several disks stacked on a spindle. The disks are mounted to the spindle in a spaced apart relation so that the separate disks do not touch each other. Both sides of each disk are generally used to store data.
Each disk surface is divided into portions where data is stored. There are a number of tracks situated in concentric circles, and each track in a disk drive is further subdivided into a number of sectors which is essentially just one section of the circumferential track. Disks in a disk drive are made of a variety of materials. Most commonly, the disk is made of metal or plastic. To store and retrieve data on a disk, a magnetic transducer known as a read/write head is passed over the surface of the disk.
There are two types of disk drives, rotary and linear, both of which have an actuator that holds all the transducers or read/write heads. The actuator arms move so that the read/write heads attached to the actuator arm move to locations over various tracks on the disk. Attached to the actuator arm is a coil, most commonly known as a voice coil. The voice coil and the magnets associated with it are the major portions of a motor, known as the voice coil motor, which is used to move the actuator arm.
Increasing the speed at which data can be located and retrieved using a seek operation is very desirable in a disk drive or direct access storage device. In order to optimize the seek performance of a disk drive, it is important to accurately model the various parameters within the disk drive. One of these parameters is the torque factor (KT) of the voice coil motor. In many disk drives, this KT parameter, or its inverse (1/KT) which is referred to as the compensation or adjustment factor, is used within the seek algorithm to aid optimization of the performance and reliability of the seek function. For example, the torque factor KT can and does change as a function of the position of the voice coil motor heads (i.e., which track of the disk drive over which the head is positioned). This relationship forms a curve of normalized torque factor versus disk position (the xe2x80x9cKT curvexe2x80x9d). This KT curve is commonly determined during the manufacture of the disk drive.
One of the ways to optimize seek operations of a disk drive is to adjust the KT curve by an adjustment factor during operation. Typically, this adjustment will occur during a recalibration of the disk drive or during start-up of the disk drive. This adjustment factor during recalibration or start-up (AFRECAL) is used to adjust the KT curve for changes that have occurred during disk drive operation since the last recalibration. The operation of a general disk drive and control system during track seeking and track following (the seek operation) can be found in U.S. Pat. Nos. 4,679,103 and U.S. Pat. No. 4,835,633, issued to International Business Machines Corporation, which are incorporated by reference herein.
The KT for a disk drive voice coil motor can also change as a function of temperature within the disk drive plant. Typically, as temperature increases the KT of the voice coil motor decreases (due to the effect of increased temperature on the magnets within the voice coil motor). Thus, if no corrective action were taken, the seek time of the disk drive would increase as the temperature within the disk drive plant increased.
Providing KT values that have been further adjusted based on changes in temperature would provide a more optimized seek functional. However, it is very difficult or sometimes impossible to measure the KT during normal operation of the disk drive. Currently, the KT and/or temperature changes are compensated for during recalibrations of the disk drive. Recalibrations within a disk drive to adjust for important plant factors, such as sensor gain and torque factor, occur at certain times as defined in the microcode operating the disk drive. Recalibrations are very typically done automatically upon the occurrence of certain events such as start up of the disk drive and during automatic recovery operations. Existing disk drives can use the recalibrated KT within the seek algorithm to more accurately model the disk drive.
This prior method of recalibration in order to compensate for torque constant for changes in temperature has several disadvantages. One of the disadvantages is that performing a recalibration is a relatively difficult and time-consuming operation that interrupts the general flow of data to/from the disk drive and decreases the overall disk drive performance. Performing a recalibration specifically for changes in temperature, while increasing seek performance, would reduce the overall performance of the disk drive.
The present invention provides an improved torque factor correction system and method that substantially eliminates or reduces disadvantages and problems associated with previously developed systems and methods used for compensating a voice coil motor torque factor due to changes in temperature.
More specifically, the present invention provides a system and method for compensation for variation in voice coil motor torque factor due to changes in temperature to improve the seek performance of a disk drive.
As previously discussed, the curve relating torque factor to position, or the KT curve, is determined during manufacture and can be adjusted at each recalibration or at each start-up operation by an adjustment factor (AFRECAL). The AFRECAL can be used to adjust the KT curve for changes that have occurred during disk drive operation.
The system and method of the present invention further improve the seek operation by further adjusting the KT curve compensation for changes in temperature during operation of the disk drive without having to perform a recalibration. The present invention uses a numerical relationship between change in torque factor and change in temperature (G) for the voice coil motor, combined with the torque factor adjustment and temperature at/near the voice coil motor measured at a first time (for example during the initial start-up of the disk drive during the automatic recalibrations that is performed during a start-up), AFRECAL and TRECAL respectively, to determine an adjustment factor (AFEVENT) that is used to adjust the most recent KT curve for temperature changes during operation. The ARECAL is simply an adjustment of the curve that relates torque factor to position.
The AFRECAL and TRECAL are stored in memory. At some later predetermined interval or event, the temperature at or near the voice coil motor is again measured (i.e., xe2x80x9cTEVENTxe2x80x9d). From these known temperature and torque factor adjustment parameters, in combination with the known relationship between temperature and torque factor (G) and position and torque factor (KT curve) for the voice coil motor, a temperature-compensated adjustment factor at the future time/event (AFEVENT) can be calculated. This new AFEVENT can be applied to the KT curve to provide a temperature-compensated KT curve that has been adjusted for temperature. KT values from this new KT curve are now used in the seek algorithm in place of the original KT values to provide more optimal seek performance.
The present invention provides an important technical advantage of improving the seek performance for disk drives without having to perform a recalibration operation.
The present invention provides another technical advantage by reducing the number of seek errors.
The present invention provides yet another technical advantage by providing an improved seek performance of the disk drive after changes in temperature, as compared to the seek performance of the disk drive without any temperature compensation.